I think oils improve with age and can take handling also to a degree , all plastic degrades under uv light , just look at the first generation upvc windows going grey , next stage is the breakup of the plastic , which I am beginning to see on facia and soffit boards .
Once covered a pallet of bricks with 1000 gauge polythene , left for a year in my back garden and awoke one day to find the poly in thousands of fragments UV monster hit